The present invention relates to a foam molding comprising a skin coating film formed by the in-mold coating method and a urethane foam body obtained by reaction injection molding (said foam molding being hereinafter referred to as xe2x80x9cRIM foam moldingxe2x80x9d). In more particular, the invention relates to RIM foam moldings which, when used for the ring part or the spoke part of steering wheels or the like, permit easy removal of flashes therefrom.
RIM foam moldings are in wide use in steering wheels for vehicles, such as automobiles and the like, horn pads, arm rests, etc.
For example, a ring part 10 of a steering wheel is produced by covering a ring part core bar 12 with a urethane foam body 14 (usually semi-rigid) having a flexible, integral skin and further, to enhance the light resistance and abrasion resistance, forming a skin coating film 10 on the urethane foam surface (see FIG. 1).
The above-mentioned urethane foam body is usually formed by RIM (reaction injection molding), because the mold clamping pressure in RIM is small (about {fraction (1/10)} or less of that in the injection molding of usual thermoplastic resin) and moreover the energies required for heating and cooling of the mold are also small. The above-mentioned skin coating film is in most cases formed by the in-mold coating method because of the good productivity and other merits of the method.
Thus, the ring part of a steering wheel has generally been formed in the manner described below.
(1) A skin coating film (in-mold coating film) 16 is formed by means of spray coating, etc., on the cavity surfaces 18a and 20a of a flask mold (in the example shown by the Figure, upper mold-under mold) 18 and 20 (see FIG. 2).
(2) A ring part core bar 12 is fixed to the mold in the open state, then the mold is closed, and a urethane material is poured in by injection.
(3) The urethane material is reaction-cured, and then the resulting molding is released from the mold. On the ring part 10 of the molding released from the mold, there remains a flash 22 at the position of the matching face (in other words, parting line) of the mold as shown in FIG. 3, so that the molding is finished by conducting deflating, to obtain the ring part of a steering wheel. In RIM, however, since the mold clamping force is small and the. urethane material is injected into the mold in a state of low molecular weight having a good fluidity, flashes of a large width are apt to develop at the matching face of the mold.
The urethane foam in the ring part or the spoke part of previous steering wheels has a density of about 0.7 g/cm3, but, owing to the recent requirement for lighter weight steering wheels, urethane foams of high ratio expansion type having a density of about 0.5 g/cm3 have come to be required. However, it has been revealed that when a urethane foam of high ratio expansion type is used, the flash is apt to be removed with difficulty.
In view of the above-mentioned situations, the object of the present invention is to provide a foam molding which permits easy removal of flashes even when it is a foam molding of high ratio expansion type.
The present inventors have made extensive study to solve the above-mentioned problems and, in the course of the study, have found that when a skin coating film which has a small elongation at break is used in the foam molding, the flash can be easily removed. On the basis of the above finding, the present inventors have arrived at a reaction-injected foam molding having the structure described below.
Thus, the foam molding of the present invention comprises a skin coating film formed by the in-mold coating method and having an elongation at break of 20 -200% (JIS K 6400; No. 1 dumb-bell test specimen) and a urethane foam body obtained by reaction injection molding and having a density of 0.35-0.60 g/cm3.